Galvanic Isolators, Polarity Indicators, AC & DC Wiring

The galvanic isolator is a very simple device. It keeps stray currents that can cause galvanic "corrosion" away from a boat. It allows AC to pass through, but with the use of two diodes in series, in each direction, the isolator blocks any voltage (AC or DC) with voltage less than about 1.4 Volts, either polarity (they say about 1.1 volts, but they are conservative in their rating, as typical silicon diodes need to be forward biased about .7 volts before they will conduct). All this means is that there needs to be an AC fault greater than 1.4 volts for the galvanic isolator to conduct the fault current to the AC safety ground on shore. There is also a capacitor across the diodes that will also pass (depending on its size, but probably small) AC currents to shore ground. See the diagram in the Word doc "Galvanic Isolator Diagram". The pdf file "AC wiring diagram" shows how my isolator is installed.

The job of the Reverse Polarity Indicator (RPI) is to determine if there is voltage potential between Safety Ground and Neutral. Shore power brings 3 (4 for 250v) leads into the boat -- the hot lead, the neutral, and the safety ground (250v has two hot leads of 125v each). The RPI indicates if the lead that should be neutral is, in fact, hot. This indicates a dangerous situation as only the hot lead is normally switched. If the RPI light is on, unplug from shore power. See the Word doc "Reverse Polarity Indicators" and the AC wiring diagram mentioned above.

I have completely (save for a few lamp wires that are under the hull liner) rewired my boat -- both AC & DC. I also added 50-amp 125v power -- I use a pigtail to convert the 250/125 power available at the dock power pedestal to the 50a 125v I want in the boat. See the files "Pigtail Internal Wiring" and the AC wiring diagram. All the pigtail does is isolate one of the 250v hot leads.

Click here to view the related documents.

• ABYC Shore Power Ground Specs
• My AC wiring diagram
• My DC house power wiring diagram
• A galvanic isolator wiring diagram
• 250v to 125v pigtail internal wiring
• Reverse polarity wiring diagram

The images below show the old and the new AC wiring. The old wiring was awful.

All grounds (DC, Bonding System, 30a AC, and 50a AC are common. See the Word doc, "ABYC shore power ground spec".

The pdf file, "DC house power" shows the 12v wiring.

In the process of rewiring the AC and adding 50a, I replaced the original power panel with a new one. The old panel is shown below, followed by images of the front and back of the new panel. The teak trim that is removed in the photo covers the cut-away section of fiberglass. The new panel has ELCI (Equipment Leakage Circuit Interruptor) breakers on the 30a and 50a AC power. The white switches are 30a AC; the red switches are DC; the black switches are 50a AC. All switches (breakers) have indicator lights.

Below are some images indicating plug polarity that may be of interest.